Papilledema is being studied at the clinical, histologic and ultrastructural levels by contrasting the effects of increased intracranial pressure and decreased intraocular tension in experimental models. A model of papilledema in rhesus monkey was created by irradiating the occipital lobe with a single dose of 3,500 rad of X-irradiation. The various physiologic and pathologic parameters of this model are currently being studied. Our pathologic study showed that papillede@a so produced consisted of extraocular edema as well as axonal swelling. A second model of papilledema by lowering intraocular tension is being investigated. The pathology of these animal models are being compared with that of human on file at the Registry of Ophthalmic Pathology.